The present invention relates to systems for automatically detecting deviations in tire inflation pressure from a desired value.
It is important that the tires of a motor vehicle remain properly inflated. When the tires of a motor vehicle are under-inflated, they provide greater rolling resistance and therefore reduce the fuel economy obtainable with the vehicle. Under-inflated tires also experience greater flexing than properly inflated tires, leading to a decrease in usable tire life. For these reasons, then, tire pressures should periodically be checked to verify proper tire inflation.
Traditionally, inflation pressure of the tires of a motor vehicle has been checked by stopping the vehicle and manually applying a tire pressure gauge to each tire in turn. Motor vehicle operators are often lax in performing this procedure, however, either because they are unaware of the disadvantages of under-inflation of the tires, are unschooled in the procedure used for checking tire inflation, or are simply too busy or forgetful to regularly conduct tire inflation checks. As a consequence, many motor vehicles are operated with under-inflated tires. It would be desirable to provide an automatic system for monitoring tire pressure so that a motor vehicle operator would know when the vehicle's tires required re-inflation.
An automatic tire inflation monitor would also be useful in detecting flat tires. Normally, the detection of flat tires is a trivial exercise since a flat tire has an immediate and noticeable influence on the handling characteristics of the vehicle. This is not always the case, however. A new type of tire, referred to as a "run flat" tire, is now finding increasing use on motor vehicles. A "run flat" tire is designed to support the motor vehicle even in the event of a significant loss in tire pressure, thereby permitting the vehicle to be driven for a short distance without changing the tire. Unlike a flat in a conventional tire, a flat in a "run flat" tire may not be readily perceptible to the motor vehicle operator. An automatic system for warning the operator of the flat would therefore be useful.
Fluid pressure is usually monitored by in situ pressure sensors. Such sensors cannot be conveniently used in tires mounted on a motor vehicle, since the tires rotate. The communication of electrical signals between a pressure sensor rotating with a vehicle tire and other, nonrotating instrument components is not easily accomplished. It would be desirable, therefore, if a tire deflation warning system could be devised which did not require interfaces to the tires.